Page:Handbook of Meteorology.djvu/67

Rh of Texas, and the Norther of the San Joaquin-Sacramento Valleys are classed among the “destroyers,” from the fact that, in many localities, two or three days of their duration is fatal to growing crops.

The Santa Ana of southern California is the outpouring of a hot, dust-laden desert wind through one or more of the mountain passes. In the past thirty-five years, irrigation and cultivation have been extended into the arid region, with a result that the Santa Ana is largely deprived of its dust content and its high temperature. The Santa Ana in its old time vigor was merely the edge of a desert simoon that intruded upon nearby fertile lands. The simoon itself occurs in every desert so far as is known. It is a sand storm because of its velocity. In the Colorado and Mohave deserts the simoon may have a velocity exceeding 75 miles an hour. The Washoe Zephyr of the Basin Region of the United States, and the Khamsin of Egypt are desert winds of the same kind. They are thought to be cyclonic in character, but practically they are dust-laden winds, either blowing into a desert, or out of a desert.

The Texas Northers are biting cold winds, common to the high western plains of the United States and northern Mexico. They usually follow warm and balmy winds of southerly direction. The onset may be very sudden. A fall of temperature of 50 degrees within a day is not uncommon. The Bora and the Mistral of the Mediterranean coast of Europe are similar in character; they are cold winds sliding down the steep mountain slopes because of increasing pressure to the northward. In the southern hemisphere, the Pampero is the counterpart. It is most noticeable in the pampas, or great plains east of the Andes, and in many instances it extends to the coast. Although a southwest wind, it is classed with Northers because of its origin. The Blizzard is nominally a cold-wave wind which is sufficiently vigorous to pick up and carry loose snow; it is a northwesterly wind. Popular usage applies the name to any wind of gale force that accompanies a snowstorm.

Direction and Velocity.—The diagram of the major circulation of air shows that the normal movements of winds are